Wire, which term here is intended also to cover rod, is rolled in at least one finishing frame or stand of a wire mill. The rolled wire then passes through a cooling and/or equalizing stretch downstream of the last finishing stand in the travel direction, where the wire, which is very hot from the rolling operation, cools somewhat and its temperature and crystalline structure stabilize and become uniform. The wire is pulled through the cooling and/or equalizing stretch by means of a cooler drive typically provided at the downstream end of the cooling and/or equalizing stretch. Downstream of the cooler drive a coiler for the wire deposits the wire in turns that may overlap or form a coil on a support, typically a conveyor moving slowly downstream from the coiler. See U.S. Pat. No. 5,463,886 as well as DE 2,437,684 and DE 3,039,101.
The wire to be coiled is produced in a number of finishing stands each normally having two rollers that transversely compress (and thereby longitudinally lengthen) the workpiece as it moves downstream until it has the desired diameter. Since the transverse compression lengthens the wire, it leaves the train of rolling stands or stands at a relatively high travel speed.
Typical prior-art systems are shown in FIGS. 1 and 2. Here a wire mill 3 has a number of rolling stands 2 that function as described above to produce a wire 1 that exits the furthest downstream stand 2 at the desired caliber and at a travel speed VD. Then the wire 1 travels downstream in a travel direction F through a straight stretch 4 in which it is cooled, the wire's temperature becomes uniform throughout its cross section, and its structure stabilizes.
The wire 1 is pulled through the stretch 4 by a cooler drive 5, typically formed as a pair of rolls or a capstan that grip the wire 1, at the speed VD. FIG. 2 shows how a second cooler drive 5′ can be provided roughly in the middle of the cooling/equalizing stretch 4 to maintain the wire speed at VD and to keep the wire 1 tensioned as it cools.
Downstream in the direction F from the cooler drive 5 the wire is passed to a coiler 6 that deposits it in turns forming a coil on an output conveyor, table, or the like.
The problem is that the wire travel speed VD is not constant but varies inherently because of the nature of producing wire by rolling, where combined factors of tension and compression are used to produce a product whose size must comply with exact standards. Thus the rolls of the stands 2 are normally driven by meticulously controlled drives that operate with feedback from upstream and downstream sensors so that the finished product is perfect, albeit moving at a somewhat varying speed VD that, as mentioned above, must vary. Even the cooler drive 5 is normally controlled to operate at varying speed to maintain the wire 1 under tension in the stretch 4.
As a result the turns produced by the coiler 6 are not uniform. When the wire 1 is moving too rapidly, the diameters of the turns are too large, and when it is moving too slowly they are too small. Since the speed VD varies during production, for instance as the equipment heats up, it is therefore impossible to produce coils of uniform size.